Add if-/else query to give an error message and add two sentences in pdf-output in perlscript

Hi Freelancer, I have a small project. After years we found an error in our script. Well, we could not find the error inside the script. The script is from 2008. The script makes calculations for tarps with given sqaremeter and prices for different products. For very small sizes under 4 sqaremeter we have our starting price. It runs all very well. But sometimes customers are coming with an offer, made from the tool for 57 bucks for example for a very big tarp because they have made that with our script. When I put in the same sizes I will get a different calculation. I did not find the error. We save the calculations inside a database. And indeed there are calculation with the same values but different value for sqaremeter: "0" and therefore a very bad price, our starting [login to view URL] 57 bucks is the starting price and in my printed calculation I have a printed result with the calculated sqaremeter. But the sqaremeter calculated is "0" and the price is the staring price for a tarps would costs much more. What I want is to fix the error or making an if-/else query to give out an error message when sqaremeter in the result is "0" and to add two sentences at the end of the pdf-output inside the perl script with sample text for later changing. I am online. Please ask me. Enclosed a file with the main-code but without database-values. You can see it online: [login to view URL] It is all in German language. It is very simple.